This invention relates to an arm mechanism for a pushbutton type tuner ameliorating dimensional precision.
The broadcast station selecting mechanism in car radios is so designed that both manual and automatical selections are possible and a special arm mechanism for automatic selection is disposed therein. The arm mechanism is utilized in order that, when a station has been once selected by means of a manual tuning knob, the tuned frequency is memorized by its position on a memory slider, which is moved in synchronism with the tuning knob.
FIGS. 1(a) and 1(b) show such an arm mechanism, in which 1 denotes a pushbutton; 2 represents an arm plate, an end of which is inserted by force into the pushbutton 1, for supporting rotatably a frequency defining plate 3, and 4 is a plate spring mounted on the arm plate 2 and having a pair of branches 4A and 4B, the free ends of which are inserted by force into the pushbutton 1, thus locking the frequency defining plate 3. The frequency defining plate 3 is a cam having a frequency defining pin 5 at its extremity and mounted rotatably on the arm plate 2 by a setting pin 6. 7 and 8 are pins for fixing the plate spring to the arm plate 2.
In the above-described mechanism, prior to automatic selection, when the memory slider 9 disposed on the plate spring 4, which is moved in synchronism with the (not shown) tuning knob, is in a tuning position and the pushbutton 1 is pushed, the frequency defining plate 3 gets under the memory slider 9. At the same time the frequency defining pin 5 is guided by a wave shaped guide 10 and advances in a valley of the wave shaped guide. A procedure for memorizing a tuned frequency is then accomplished by the fact that the frequency defining pin 5 is held between the branches 4A and 4B (locked). After this procedure has been once done, for automatic selection it is enough to push the pushbutton 1. Even if the memory slider 9 is at a random location, since the wave shaped guide 10 is guided by the locked frequency defining pin 5, the memory slider 9 is returned to the memorized original location, and thus the broadcast station, whose frequency has been beforehand tuned, is selected. Thus, by disposing so many pushbuttons that their number corresponds to that of broadcast stations to be selected, it is possible to select arbitrarily desired one.
Furthermore, in such an arm mechanism, a projection (pin) 11 is disposed at the base part of the arm plate 2, which projection 11 is guided by a slit 12 disposed in the frame body of the radio so that the arm plate 2 is able to go backward and forward.
This projection 11 has been heretofore formed, as indicated in FIG. 2, by embossment. That is, the projection 11 has been formed by using a punch 14 from the upper surface of a plate 2', of which the arm plate should be made, held on a die 13.
In this case, since the projection 11 has been worked only from one side, a tapered portion 15 has been inevitably formed at the periphery of the projection 11 and therefore it has been difficult to obtain a high dimensional precision. By this reason it has been difficult that the arm plate 2 goes backward and forward with a high precision in the slit 12 and consequently tuning has tended to deviate.